It is well known to fabricate mutiple layers of metal conductors embedded in a dielectric material and supported therein for connecting the conductors to various electrical components such as semiconductors. For example, a multiple layer electrical interconnect system may include conductors extending in the X, Y and Z directions including through via conductors in a multilayer sandwich embedded in a dielectric of continuous anodic aluminum. However, the anodic aluminum, Al.sub.2 O.sub.3, has a rather higher dielectric constant than is desired for very high speed interconnect transmission lines.
The present invention is directed to a method of removing the bulk of the anodic aluminum by masking and etching thereby leaving pillars of anodic aluminum in order to support the metal conductors and for surrounding the major portions of the conductors with air which has a low dielectric constant.